This invention relates to a system and method for measuring a parameter of interest in a processing stream. In particular, the invention relates to the use of near infrared spectroscopy for the on-line measurement of a parameter of interest in a processing stream. More particularly, the invention relates to the use of near infrared spectroscopy for the on-line measurement of parameters of interest in sugar cane processing.
Processing of biological material such as plant material usually involves measuring parameters of interest in the starting material and through to the desired end product or products. The measurement of the parameters can be for process control or for monitoring the level of a component in the material.
Measurements are typically made on samples taken from the processing stream. Depending on the parameter being measured, there can be a delay in determining the value of a parameter, as a consequence of which the parameter is not determined in real time. Furthermore, a sample may not be truly representative of the bulk of the material being processed at the point of sampling.
There can be other difficulties with measuring parameters of interest in a processing stream by sampling. A particular field where such difficulties occur is sugar cane processing. Sugar and related products are provided by processing sugar cane in sugar mills where the cane is crushed and processed through to crystalline raw sugar and molasses. The cane is supplied by plantation owners or individual cane farmers with the owners or farmers being paid for the cane supplied on the basis of tonnage and quality.
In Australia, for example, the amount paid to a plantation owner or farmer for each parcel, of the supplied cane is determined by weighing the parcel and evaluating the sugar content of the cane. An industry-agreed value is then used to calculate the amount paid for the parcel, the whole process being referred to as the xe2x80x9ccane payment schemexe2x80x9d. Various systems are used to determine the sugar content of the supplied cane. Each of the systems requires sampling, sample processing and analysis. In many countries, a core of cane is withdrawn from the delivered cane, processed by pressing or wet disintegration to juice which is analysed and converted to a measure of the sugar content of the cane.
The system used in Australia requires analysis of the earliest juice (first expressed juice) driven out of the cane crushing rollers. This entity has been shown to be convertible to and representative of the analysis of the whole cane. The cane payment system requires continuous sampling of the first expressed juice throughout the period of crushing each parcel of cane and an analysis reported for that parcel. Payment is based on this analysis and the weight of the parcel. The juice is subsampled and analysed according to standard proscribed methodologies for xe2x80x9cpolxe2x80x9d (a measure of the sucrose content of the juice) and xe2x80x9cbrixxe2x80x9d (a measure of the dissolved solids content of the juice). The estimation of the total cane supply is determined by means of the first expressed juice analysis, the fiber content of the cane and empirically determined relationships linking the juice analysis and total cane analysis.
The fiber analysis of the cane for which the juice is sampled is determinable by washing a representative sample of the cane free of dissolved solids. The sample is prepared by cutter grinding to an appropriate fineness prior to washing. Sampling and analysis for individual parcels is not practical and a deemed fiber is used in calculations on an individual farmer""s cane delivery.
Each variety of cane is allocated to one of two or three classes of more or less common average fiber composition. The deemed or xe2x80x9cclass fiberxe2x80x9d as it is termed is a rolling average of the fiber of the class which has been allocated to the cane variety. The rolling average is obtained by regular sampling of each class throughout the day, compositing within the class and determination of the daily average fiber. Several days analyses are combined in the rolling average.
The use of class fiber is a particular weakness of the current system but is forced upon the system by financial and practical impossibility in providing a representative, meaningful individual fiber composition for each parcel of cane. Providing such representative and meaningful data in a typical Australian sugar mill would require the analysis of at least 150 parcels of cane each day, in duplicate, requiring a sampling team of approximately 30 persons, approximately 20 fiber analysing instruments and 4 to 5 cutter grinding machines.
The class fiber system also makes no distinction between the actual condition of the particular parcel of harvested cane in respect of dirt and extraneous matter content or in respect of inherent differences that may pertain to its plant or ratoon status.
Cane analysis is labour intensive and relies on extended sampling procedures, analysis and subsequent conversion to an estimate of the analysis of the whole cane received. The methodology in practical use does not give adequate feedback to the grower on cane quality or adequate feed forward for process control to the miller as it does not use individual parcel fiber analyses in the compositions.
Spectroscopy is a technique whereby a chemical compound can be identified by the degree of modification to light at different frequencies or wavelengths. Near infrared spectroscopy (NIR)xe2x80x94that is, spectroscopy where absorption of light over the range 400 to 2500 nm is analysedxe2x80x94has been previously applied as a tool in such fields as the measurement of protein and moisture in grain, the composition of forage for animal food, the degree of ripeness of fruit and the composition of fine cane particles, cane juices, syrups and sugars in sugar laboratory situations. However, NIR has not previously been exploited on-line for measuring parameters of interest in a processing stream such as comminuted sugar cane during cane processing.
The object of the invention is to provide a system and method for the on-line measurement of parameters of interest in a processing stream, which system and method utilise near infrared spectroscopy. A particular object of the invention is to provide a system and method for the on-line measurement of parameters of interest in sugar cane during processing of the cane utilising near infrared spectroscopy.
According to a first embodiment of the invention, there is provided a system for the on-line measurement of a parameter in a processing stream, the system comprising:
(a) a scanning head mounted adjacent a continuous stream of processed material, the scanning head comprising a remote light source and reflected light gathering and transmission apparatus;
(b) a near infrared spectrophotometer which includes a monochromator for resolving the reflected light into light of a discrete wavelength;
(c) a database containing a reference calibration equation linking absorption characteristics by wavelength and the quantified presence of the parameter of interest; and
(d) a computer for measuring the parameter by application of the calibration equation to the obtained spectrum for a sample and managing said system.
According to a second aspect of the invention, there is provided a method of on-line measurement of a parameter in a processing stream, the method comprising the steps of:
(i) obtaining an infrared reflectance spectrum from a stream of processed material;
(ii) applying an appropriate calibration equation to the spectrum to quantify the presence of the parameter of interest; and
(iii) statistically validating the spectrum obtained as being represented by the calibration equation.
According to a third embodiment of the invention, there is provided a system for the on-line measurement of a parameter in processed sugar cane, the system comprising:
(a) a scanning head mounted adjacent a continuous stream of processed cane, the scanning head comprising a remote light source and reflected light gathering and transmission apparatus;
(b) a near infrared spectrophotometer which includes a monochromator for resolving the reflected light into light of a discrete wavelength;
(c) a database containing a reference calibration equation linking absorption characteristics by wavelength and the quantified presence of the parameter of interest; and
(d) a computer for measuring the parameter by application of the calibration equation to the obtained spectrum for a sample and managing said system.
According to a fourth aspect of the invention, there is provided a method of on-line measurement of a parameter in processed sugar cane, the method comprising the steps of:
(i) obtaining an infrared reflectance spectrum from a stream of said processed cane;
(ii) applying an appropriate calibration equation to the spectrum to quantify the presence of the parameter of interest; and
(iii) statistically validating the spectrum obtained as being represented by the calibration equation.
The term xe2x80x9con-linexe2x80x9d as used in the above definitions of embodiments and hereafter denotes measurement at the actual process stream as well as measurement on a portion of the stream of material being processed through a by-pass line. The second of the meanings given in the preceding sentence is commonly referred to as an xe2x80x9cat-linexe2x80x9d measurement.
The term xe2x80x9cprocessing streamxe2x80x9d as used in the definitions of the first and second embodiments of the invention denotes a stream of material derived from plants wherein the plant, or a part thereof, has been comminuted. Alternatively, plant-derived material can be material that has been extracted from a plant, or part thereof, by procedures such as slicing, dicing, shredding, mincing, pulping, pressing, sawing or rasping. The processing stream referred to in these embodiments thus includes, but is not limited to, prepared or comminuted sugar cane, sliced sugar beet, crystal sugar, bagasse at various stages, silage and processed grains, fruit and vegetables as well as processed fruit and vegetables, particle board and paper.
It will be appreciated from the foregoing description of the third and fourth embodiments that the invention allows on-line assessment of cane quality providing, in contrast to present measurement systems, meaningful fully representative information. Parameters of interest which can be measured using the system and method of the invention include fiber content, juice brix or dissolved solids content, juice polarisation or sugar content, commercial sugar content or CCS of cane, water, and other quality parameters such as ash which is related to dirt content, individual inorganic elements, and process parameters such as pol in open cells. The inorganic parameters that can be measured include the following: phosphate; nitrogen; calcium; magnesium; potassium; iron; and, silicon. Extraneous matter such as dirt, tops, trash and suckers can also be measured.
The term xe2x80x9cprocessed sugar canexe2x80x9d or derivatives thereof as used herein include within their scope, prepared cane, intermediate and final crushing roller bagasse, boiler feed materials, raw sugar and crystalline sugar. Consequently, in addition to the parameters given above, other parameters that can be measured include pol, moisture, grist, filterability, starch, dextran and other polysaccharides.
The continuous stream of processed cane can be a stream included in a normal sugar milling process or can be a stream set up for analytical purposes. In other words, the invention is not restricted in application to the milling process per se. An example of a stream set up for analytical purposes is processed cane from core samples of cane batches, which samples are processed in a mill""s analytical laboratory.
A requirement of the stream, however, is that the material be devoid of gross voids so that the scanning head sees an essentially unbroken layer of the processed cane. If necessary, the conduit or the like carrying the stream can be constricted to effect a compression of the material passing the scanning head.
In the system and method of the invention, the scanning head is mounted at a fixed distance from the surface of the processing stream, which, in the case of the third and fourth embodiments, is a stream of processed cane. The distance between the surface of the processing stream and the scanning head is usually fixed within the range of 75 to 100 mm with the distance maintained at xc2x15 mm. Maintenance of a set distance is necessary for accurate application of calibration equations to parameter measurement.
As an example of the mounting of the scanning head in sugar cane processing, the head is mounted at the feed chute for the first crushing mill of a raw sugar mill. Other suitable positions for mounting the scanning head on equipment included in a sugar mill will be detailed below.
A suitable cradle may be required for mounting the scanning head to insulate the head from vibration present in the equipment comprising the process. This is particularly the case with sugar milling equipment. Temperature control is also advantageous such as by mounting the scanning head in an air-conditioned chamber. As a window has to be provided for light transfer between the scanning head and the processed cane, the sensing head cradle preferably allows repositioning of the sensing head so that the window glass can be removed for cleaning or replacement. Cleaning or replacement of the window glass is necessary as debris from a processing stream such as processed cane passing the window can build up on the glass or damage the glass, interfering with operation of the system.
The spectrophotometer is preferably remote from the scanning head but linked thereto by a fiber optic cable. The spectrophotometer, like the sensing head, is vibration and temperature insulated if necessary. When remotely located, the requirements of the vibration insulation means in respect of the spectrophotometer are not as stringent as for the sensing head. However, the sensing head and spectrophotometer can be an integral unit in which case the vibration and temperature insulation must meet the requirements of the sensing head. Any insulated chamber housing the spectrophotometer is advantageously airconditioned.
The spectrophotometer can be any suitable commercially available instrument. An example of a suitable instrument is Foss NIRSystems Model 6500 system incorporating a Model 6500 monochromator, Direct Light Reflectance System and ISI NIRS3 or Vision Software supplied by Foss NIRSystems Inc, 121021 Tech Rd, Silver Spring, Md. 20904, USA. This instrument has a scanning range of 400 to 2,500 nm. However, another suitable instrument is the NIRSystems Model 5000 which operates over a wavelength range of 1,100 to 2,500 nm.
The database calibration equations referred to in section (c) of the above definitions of the first and third embodiments can be determined by the gathering of reflectance spectra on the material present in the processing stream and statistically evaluating the data using a routine laboratory assay of the parameters of interest on concomitant samples of the material. A minimum of 200 assay samples are generally required for equation development and inclusion in the database. The interfaced computer referred to in section (d) of the first and third embodiments serves to link the analytical system with the individual user of the data or the dependent processes. In the case of prepared cane, it is necessary that the instrument be linked to the cane sample tracking system to provide cane parcel identification for the cane being scanned and to have the capability of inserting the result of the computations for parameters of interest into the files in the cane payment system for the relevant parcel of cane. The computer software advantageously has the capability of delivering analytical data to process controllers in real time.
The calibration equations are crucial to the operation of the system and the method but can nevertheless be developed by one of ordinary skill in the art, particularly with the guidance of the NIR instrument manufacturer. The process involves the steps of collection of spectral and laboratory data, population structuring, calibration development and finally, validation of the equation. It is essential that the link between the spectral data and the corresponding laboratory analysis is strong. Using sugar cane processing as an example, the spectral data is collected by scanning the portion of cane as it passes the read head, collecting all spectra associated with that portion and averaging them to produce a single spectral result for that portion. The corresponding laboratory sample, in the case of calibration for fiber, is obtained by taking small snap samples from the process stream over the whole length of the portion. These snaps are thoroughly mixed to produce an average laboratory sample, which is then sub-sampled for analysis by a laboratory can fiber machine or a laboratory bag fiber analysis procedure. A minimum of 200 such pairing of analyses of portions of cane are required to produce a preliminary equation. To produce a robust global equation, cane should be sampled which contains as much as possible of the likely variation in cane. The calibration software is used to determine the population boundaries of the calibration set which is necessary to define the spectra which are represented by the calibration equation to be developed. Spectra three standard deviations from the mean spectral result are discarded. The software selects the calibration set and the validation set from the spectra and their laboratory results. The calibration equation is developed from the calibration set using, for example, partial least squares calibration mathematics. The equations are validated, firstly, by applying the equation to the validation set and then in an on-line situation with spectra that were in no way associated with the calibration process.
A xe2x80x9clocalxe2x80x9d calibration technique can also be employed. This calibration technique uses the library developed in the population structuring step in an on-line situation to select similar spectral results to an unknown spectrum obtained from a scan. These spectra and results are used to develop an equation which is then applied to the unknown spectrum. This approach is particularly effective in a system of networked spectrophotometers employing the advantages in robustness of the global calibration with the precision of a local calibration.
As indicated above in the definition of the second and fourth embodiments, a preliminary step in the method of the invention is the obtainment of an infrared reflectance spectrum of the processing stream containing the parameter of interest. An objective in this step is to minimise the time taken to complete a scan so that more scans which are, in effect, sub-samples can be taken during the measurement of a particular parameter during the processing of a portion of material of interest.
Using measurement of a parameter in processed sugar cane as an example, scanning of a sample is initiated on receipt of instructions from a computer controlling the scanning operation, which computer is also central to the execution of the method. The term xe2x80x9csamplexe2x80x9d in the foregoing context denotes the measurement of a parameter in a particular portion of the processed material and in determining parameters in crushed cane, this portion will be what is referred to as a xe2x80x9cparcelxe2x80x9d or a xe2x80x9crakexe2x80x9d of cane. In a typical scan of about 36 seconds duration, about 26 seconds is taken up in acquiring up to 32 full spectral passes and 9 to 10 seconds for signal transfer. Scan frequency can be increased to allow more time for scanning the process material. The signal to noise ratio is optimised by assessing individual scans and corrupted scans discounted. Corruption, for example, can be due to voids in the crushed cane passing the scanning head.
Depending on the time taken for a parcel to pass the scanning head, any scans obtained can be computed with the calibration equations and the results averaged to give a representative parameter value for the parcel.
The computer referred to in sub-paragraph (d) of the definition of the first and second embodiments can also serve to manage signals received thereby and in presentation of appropriate information from the database. It will be appreciated that normally there would be interest in more than one parameter in the processing stream. Consequently, the database must hold a reference calibration equation for each of those parameters. For example, in sugar cane processing, % fiber, brix and % water are measured in the initial crushed cane. Spectral integrity is checked and the validity of predicted results can be assessed by determining that the sum of these values is 100xc2x15. The computer, through its control program, liaises with the mill""s cane payment and process control computers taking current information and monitoring scanning conditions. It initiates a scan through the scan program when conditions are conducive. The scan program starts the instrument scan and receives the spectrum when the scan is completed. The scan program is used to apply the calibration equation for the component of interest to calculate a result from the spectrum which is passed to the control software with its evaluation of the conformity of the spectrum obtained to the spectra in the calibration set. The control software inspects and validates the results. If the result is accepted, it updates process control signals and cane payment details, computing averages for the rake when the rake ends and passing average results from accepted scans to the cane payment computer.
In the method of the second and fourth embodiments of the invention, step (iii) can additionally comprise calling for physical sampling should a measured spectrum lie outside the range predicted by a calibration equation. That is, if an unusual spectrum is obtained, a sample can be obtained for measurement of the parameter of interest by routine analytical procedures.
The system according to the first and third embodiments of the invention can be incorporated into a network. In such a network, a centralised database provides reference calibration equations to other processing streams in the network. Further, provided that instruments are standardised against the instrument on which the calibration equations were developed, the latter instrument can be used as a master instrument within the network. Global reference calibration equations provide a calibration which is robust to changes in processing stream characteristics, avoiding taking additional calibration samples and is a feature of the network arrangement.
A network of systems according to the invention is particularly advantageous in measuring parameter of interest in sugar cane processing. In this industry, sugar mills in particular region may be part of a network. Application to the network of a system according to the third embodiment facilitates operation of the mills, with fully interchangeable instruments, in such a manner as to use common calibration equations or allow access to a suitable equation from the network to apply to cane with unfamiliar characteristics and is particularly advantageous for the cane payment system discussed above.